Sj410 compression test results

[Sj410red]

Hi chaps, I've just done a compression test on my sj and it's a steady 140 to 150 psi on all 4 cylinders when engine was cold. I only removed 1 plug at a time in turn tho if that would effect results tho? So my question is, are the results ok at that reading? I'm running it up to temp now to repeat test, will post results soon. All comments much appreciated and thank you.

[Sj410red]

Engine run up to temp results are 150 to 160, this test was with all plugs removed, any views?

[Rhinoman]

Its a little bit low but I would leave it alone. Did you have the throttle fully open and the battery fully charged?

[Sj410red]

Yes foot flat on throttle and it's recently a new battery

[Sj410red]

Since I did the oil change it's been smoking on start up, which I guess is valve stem seals, could this reduce the readings by much?

[Rhinoman]

The valve seals won't make any real difference to the compression, personally I'd try to replace them without removing the head.

[Tonypp]

The valve seals won't make any real difference to the compression, personally I'd try to replace them without removing the head.

Is it possible to replace valve seals without removing the head?

[Sj410red]

From what I've read on here it can be done just a bit fiddly tho.

[Rhinoman]

Its usually done with the compressed air these days but there are old tricks like using string.

[courior]

Sorry to revive an old post.. But I have the exact same thing happen on my 410. After an oil change it smokes on startup. Why would new oil make it past the stem seals and not old oil??

I've seen vids on doing this with the head on.. Seems pretty simple if a bit fiddly. But ateast you don't have to risk knocking the timing out etc..